Polyisocyanates containing sulphonic acid groups are already known and are described, e.g., in German Offenlegungsschriften Nos. 2,227,111; 2,359,614; 2,359,615; 2,524,476 and 1,939,911. In their preparation, liquid multi-component mixtures of aromatic polyisocyanates are mixed with sulphur trioxide or an equivalent quantity of oleum, sulphuric acid or chlorosulphonic acid and left to react.
Polyisocyanates containing phosphonate groups are also already known and are described, e.g., in German Offenlegungsschrift No. 1,127,583. These phosphorus-containing isocyanates may be prepared, for example, by converting polyisocyanates into carbamic acid halides by the action of hydrogen chloride and then reacting these carbamic acid halides with equivalent quantities, based on the carbamic acid halide groups, of trialkyl phosphites by an Arbusow-type reaction.
Polyisocyanates which contain both sulphonic acid groups and phosphonate groups, however, have not hitherto been known. It is therefore necessary, for example, when producing inorganic-organic synthetic resins as described in German Offenlegungsschrift No. 2,227,147 to increase the flame-resistance of these synthetic resins by adding unreactive low molecular weight phosphoric acid esters such as trichloroethyl phosphate during the manufacturing process. This method has, however, serious disadvantages in that, if the desired mechanical properties are to be obtained, only limited quantities of these low molecular weight compounds, insufficient for providing complete flame-resistance, may be added. Moreover, the low molecular weight compounds added tend to migrate from the synthetic resin due to their low molecular weight.
It was therefore an object of the present invention to provide new polyisocyanates containing both sulphonic acid groups and chemically fixed phosphorus. This problem could be solved by the process according to the invention, which is described below.